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Bryniarski MA, Sandoval RM, Ruszaj DM, Fraser-McArthur J, Yee BM, Yacoub R, Chaves LD, Campos-Bilderback SB, Molitoris BA, Morris ME. Defining the Intravital Renal Disposition of Fluorescence-Quenched Exenatide. Mol Pharm 2023; 20:987-996. [PMID: 36626167 PMCID: PMC9907348 DOI: 10.1021/acs.molpharmaceut.2c00671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Revised: 12/13/2022] [Accepted: 12/14/2022] [Indexed: 01/11/2023]
Abstract
Despite the understanding that renal clearance is pivotal for driving the pharmacokinetics of numerous therapeutic proteins and peptides, the specific processes that occur following glomerular filtration remain poorly defined. For instance, sites of catabolism within the proximal tubule can occur at the brush border, within lysosomes following endocytosis, or even within the tubule lumen itself. The objective of the current study was to address these limitations and develop methodology to study the kidney disposition of a model therapeutic protein. Exenatide is a peptide used to treat type 2 diabetes mellitus. Glomerular filtration and ensuing renal catabolism have been shown to be its principal clearance pathway. Here, we designed and validated a Förster resonance energy transfer-quenched exenatide derivative to provide critical information on the renal handling of exenatide. A combination of in vitro techniques was used to confirm substantial fluorescence quenching of intact peptide that was released upon proteolytic cleavage. This evaluation was then followed by an assessment of the in vivo disposition of quenched exenatide directly within kidneys of living rats via intravital two-photon microscopy. Live imaging demonstrated rapid glomerular filtration and identified exenatide metabolism occurred within the subapical regions of the proximal tubule epithelia, with subsequent intracellular trafficking of cleaved fragments. These results provide a novel examination into the real-time, intravital disposition of a protein therapeutic within the kidney and offer a platform to build upon for future work.
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Affiliation(s)
- Mark A. Bryniarski
- Department
of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical
Sciences, University at Buffalo, 304 Pharmacy Building, Buffalo, New York 14215, United States
| | - Ruben M. Sandoval
- Department
of Medicine, Indiana University, Indianapolis, Indiana 46202, United States
| | - Donna M. Ruszaj
- Department
of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical
Sciences, University at Buffalo, 304 Pharmacy Building, Buffalo, New York 14215, United States
| | - John Fraser-McArthur
- Department
of Pharmacy, University of Rochester Medical
Center, Rochester, New York 14642, United States
| | - Benjamin M. Yee
- Department
of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical
Sciences, University at Buffalo, 304 Pharmacy Building, Buffalo, New York 14215, United States
| | - Rabi Yacoub
- Department
of Internal Medicine, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York 14203, United States
| | - Lee D. Chaves
- Department
of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical
Sciences, University at Buffalo, 304 Pharmacy Building, Buffalo, New York 14215, United States
- Department
of Neurosurgery, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York 14203, United States
| | | | - Bruce A. Molitoris
- Department
of Medicine, Indiana University, Indianapolis, Indiana 46202, United States
| | - Marilyn E. Morris
- Department
of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical
Sciences, University at Buffalo, 304 Pharmacy Building, Buffalo, New York 14215, United States
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Martin WP, Nair M, Chuah YH, Malmodin D, Pedersen A, Abrahamsson S, Hutter M, Abdelaal M, Elliott JA, Fearon N, Eckhardt H, Godson C, Brennan EP, Fändriks L, le Roux CW, Docherty NG. Dietary restriction and medical therapy drives PPARα-regulated improvements in early diabetic kidney disease in male rats. Clin Sci (Lond) 2022; 136:1485-1511. [PMID: 36259366 PMCID: PMC7613831 DOI: 10.1042/cs20220205] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Revised: 10/14/2022] [Accepted: 10/18/2022] [Indexed: 11/17/2022]
Abstract
The attenuation of diabetic kidney disease (DKD) by metabolic surgery is enhanced by pharmacotherapy promoting renal fatty acid oxidation (FAO). Using the Zucker Diabetic Fatty and Zucker Diabetic Sprague Dawley rat models of DKD, we conducted studies to determine if these effects could be replicated with a non-invasive bariatric mimetic intervention. Metabolic control and renal injury were compared in rats undergoing a dietary restriction plus medical therapy protocol (DMT; fenofibrate, liraglutide, metformin, ramipril, and rosuvastatin) and ad libitum-fed controls. The global renal cortical transcriptome and urinary 1H-NMR metabolomic profiles were also compared. Kidney cell type-specific and medication-specific transcriptomic responses were explored through in silico deconvolution. Transcriptomic and metabolomic correlates of improvements in kidney structure were defined using a molecular morphometric approach. The DMT protocol led to ∼20% weight loss, normalized metabolic parameters and was associated with reductions in indices of glomerular and proximal tubular injury. The transcriptomic response to DMT was dominated by changes in fenofibrate- and peroxisome proliferator-activated receptor-α (PPARα)-governed peroxisomal and mitochondrial FAO transcripts localizing to the proximal tubule. DMT induced urinary excretion of PPARα-regulated metabolites involved in nicotinamide metabolism and reversed DKD-associated changes in the urinary excretion of tricarboxylic acid (TCA) cycle intermediates. FAO transcripts and urinary nicotinamide and TCA cycle metabolites were moderately to strongly correlated with improvements in glomerular and proximal tubular injury. Weight loss plus pharmacological PPARα agonism is a promising means of attenuating DKD.
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Affiliation(s)
- William P. Martin
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Meera Nair
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Yeong H.D. Chuah
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Daniel Malmodin
- Swedish NMR Centre, University of Gothenburg, 40530 Gothenburg, Sweden
| | - Anders Pedersen
- Swedish NMR Centre, University of Gothenburg, 40530 Gothenburg, Sweden
| | - Sanna Abrahamsson
- Bioinformatics Core Facility, Sahlgrenska Academy, University of Gothenburg, 40530 Gothenburg, Sweden
| | - Michaela Hutter
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Mahmoud Abdelaal
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Jessie A. Elliott
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Naomi Fearon
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Hans Eckhardt
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Catherine Godson
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Eoin P. Brennan
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
| | - Lars Fändriks
- Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 40530 Gothenburg, Sweden
| | - Carel W. le Roux
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
- Diabetes Research Group, Ulster University, Coleraine BT52 1SA, UK
| | - Neil G. Docherty
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, D04 V1W8 Dublin, Ireland
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Martin WP, Chuah YHD, Abdelaal M, Pedersen A, Malmodin D, Abrahamsson S, Hutter M, Godson C, Brennan EP, Fändriks L, le Roux CW, Docherty NG. Medications Activating Tubular Fatty Acid Oxidation Enhance the Protective Effects of Roux-en-Y Gastric Bypass Surgery in a Rat Model of Early Diabetic Kidney Disease. Front Endocrinol (Lausanne) 2022; 12:757228. [PMID: 35222262 PMCID: PMC8867227 DOI: 10.3389/fendo.2021.757228] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 12/23/2021] [Indexed: 01/03/2023] Open
Abstract
Background Roux-en-Y gastric bypass surgery (RYGB) improves biochemical and histological parameters of diabetic kidney disease (DKD). Targeted adjunct medical therapy may enhance renoprotection following RYGB. Methods The effects of RYGB and RYGB plus fenofibrate, metformin, ramipril, and rosuvastatin (RYGB-FMRR) on metabolic control and histological and ultrastructural indices of glomerular and proximal tubular injury were compared in the Zucker Diabetic Sprague Dawley (ZDSD) rat model of DKD. Renal cortical transcriptomic (RNA-sequencing) and urinary metabolomic (1H-NMR spectroscopy) responses were profiled and integrated. Transcripts were assigned to kidney cell types through in silico deconvolution in kidney single-nucleus RNA-sequencing and microdissected tubular epithelial cell proteomics datasets. Medication-specific transcriptomic responses following RYGB-FMRR were explored using a network pharmacology approach. Omic correlates of improvements in structural and ultrastructural indices of renal injury were defined using a molecular morphometric approach. Results RYGB-FMRR was superior to RYGB alone with respect to metabolic control, albuminuria, and histological and ultrastructural indices of glomerular injury. RYGB-FMRR reversed DKD-associated changes in mitochondrial morphology in the proximal tubule to a greater extent than RYGB. Attenuation of transcriptomic pathway level activation of pro-fibrotic responses was greater after RYGB-FMRR than RYGB. Fenofibrate was found to be the principal medication effector of gene expression changes following RYGB-FMRR, which led to the transcriptional induction of PPARα-regulated genes that are predominantly expressed in the proximal tubule and which regulate peroxisomal and mitochondrial fatty acid oxidation (FAO). After omics integration, expression of these FAO transcripts positively correlated with urinary levels of PPARα-regulated nicotinamide metabolites and negatively correlated with urinary tricarboxylic acid (TCA) cycle intermediates. Changes in FAO transcripts and nicotinamide and TCA cycle metabolites following RYGB-FMRR correlated strongly with improvements in glomerular and proximal tubular injury. Conclusions Integrative multi-omic analyses point to PPARα-stimulated FAO in the proximal tubule as a dominant effector of treatment response to combined surgical and medical therapy in experimental DKD. Synergism between RYGB and pharmacological stimulation of FAO represents a promising combinatorial approach to the treatment of DKD in the setting of obesity.
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Affiliation(s)
- William P. Martin
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
| | - Yeong H. D. Chuah
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
| | - Mahmoud Abdelaal
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
| | - Anders Pedersen
- Swedish NMR Centre, University of Gothenburg, Gothenburg, Sweden
| | - Daniel Malmodin
- Swedish NMR Centre, University of Gothenburg, Gothenburg, Sweden
| | - Sanna Abrahamsson
- Bioinformatics Core Facility, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Michaela Hutter
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
| | - Catherine Godson
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
| | - Eoin P. Brennan
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
| | - Lars Fändriks
- Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Carel W. le Roux
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
- Diabetes Research Group, Ulster University, Coleraine, United Kingdom
| | - Neil G. Docherty
- Diabetes Complications Research Centre, School of Medicine, Conway Institute, University College Dublin, Dublin, Ireland
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Martin WP, Chuah YHD, Conroy E, Reynolds AL, Judge C, López-Hernández FJ, le Roux CW, Docherty NG. Protocol for a preclinical systematic review and meta-analysis of pharmacological targeting of peroxisome proliferator-activated receptors in experimental renal injury. BMJ OPEN SCIENCE 2021; 5:e100240. [PMID: 34849404 PMCID: PMC7612047 DOI: 10.1136/bmjos-2021-100240] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 10/29/2021] [Indexed: 12/16/2022] Open
Abstract
INTRODUCTION Impaired lipid metabolism in the renal tubule plays a prominent role in the progression of renal fibrosis following acute kidney injury (AKI) and in chronic kidney disease (CKD). Peroxisome proliferator-activated receptors (PPARs) are promising druggable targets to mitigate renal fibrosis by redirecting metabolism, including restoration of fatty acid oxidation (FAO) capacity. We aim to synthesise evidence from preclinical studies of pharmacological PPAR targeting in experimental renal injury, and inform the design of future studies evaluating PPAR-mediated restoration of FAO in AKI and CKD. METHODS AND ANALYSIS Studies reporting on the impact of pharmacological PPAR modulation in animal models of renal injury will be collected from MEDLINE (Ovid), Embase and Web of Science databases. Predefined eligibility criteria will exclude studies testing medications which are not specific ligands of one or more PPARs and studies involving multimodal pharmacological treatment. The Systematic Review Centre for Laboratory Animal Experimentation risk of bias tool and Collaborative Approach to Meta-Analysis and Review of Animal Experimental Studies checklist will be used to assess quality of the included studies. Data extraction will be followed by a narrative synthesis of the data and meta-analysis where feasible. Analysis will be performed separately for AKI, CKD and renal transplant models. Subgroup analyses will be performed based on study design characteristics, PPAR isotype(s) targeted, and classes of PPAR-targeting medications used. Risk of publication bias will be assessed using funnel plotting, Egger's regression and trim-and-fill analysis. ETHICS AND DISSEMINATION Ethical approval is not required. Findings will be published in a peer-reviewed journal and presented at scientific meetings. PROSPERO REGISTRATION NUMBER CRD42021265550.
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Affiliation(s)
- William P Martin
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
| | - Yeong H D Chuah
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
| | - Emer Conroy
- Biomedical Facility, Agriculture and Food Science Building, University College Dublin, Belfield, Dublin 4, Ireland
| | - Alison L Reynolds
- School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
| | - Conor Judge
- HRB Clinical Research Facility, National University of Ireland Galway, Galway, Ireland
- Translational Medical Device Lab, National University of Ireland Galway, Galway, Ireland
| | - Francisco J López-Hernández
- Instituto de Investigación Biomédica de Salamanca (IBSAL) and Instituto de Estudios de Ciencias de la Salud de Castilla y León (IECSCYL), Paseo de San Vicente, 58-182 - Hospital Virgen de la Vega, Planta 10ª, 37007, Salamanca, Castilla y León, Spain
| | - Carel W le Roux
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
- Diabetes Research Group, Ulster University, Coleraine, UK
| | - Neil G Docherty
- Diabetes Complications Research Centre, School of Medicine, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
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Abstract
The Xenopus genus includes several members of aquatic frogs native to Africa but is perhaps best known for the species Xenopus laevis and Xenopus tropicalis. These species were popularized as model organisms from as early as the 1800s and have been instrumental in expanding several biological fields including cell biology, environmental toxicology, regenerative biology, and developmental biology. In fact, much of what we know about the formation and maturation of the vertebrate renal system has been acquired by examining the intricate genetic and morphological patterns that epitomize nephrogenesis in Xenopus. From these numerous reports, we have learned that the process of kidney development is as unique among organs as it is conserved among vertebrates. While development of most organs involves increases in size at a single location, development of the kidney occurs through a series of three increasingly complex nephric structures that are temporally distinct from one another and which occupy discrete spatial locales within the body. These three renal systems all serve to provide homeostatic, osmoregulatory, and excretory functions in animals. Importantly, the kidneys in amphibians, such as Xenopus, are less complex and more easily accessed than those in mammals, and thus tadpoles and frogs provide useful models for understanding our own kidney development. Several descriptive and mechanistic studies conducted with the Xenopus model system have allowed us to elucidate the cellular and molecular mediators of renal patterning and have also laid the foundation for our current understanding of kidney repair mechanisms in vertebrates. While some species-specific responses to renal injury have been observed, we still recognize the advantage of the Xenopus system due to its distinctive similarity to mammalian wound healing, reparative, and regenerative responses. In addition, the first evidence of renal regeneration in an amphibian system was recently demonstrated in Xenopus laevis. As genetic and molecular tools continue to advance, our appreciation for and utilization of this amphibian model organism can only intensify and will certainly provide ample opportunities to further our understanding of renal development and repair.
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Xie L, Dibb R, Cofer GP, Li W, Nicholls PJ, Johnson GA, Liu C. Susceptibility tensor imaging of the kidney and its microstructural underpinnings. Magn Reson Med 2014; 73:1270-81. [PMID: 24700637 DOI: 10.1002/mrm.25219] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2013] [Revised: 02/14/2014] [Accepted: 02/19/2014] [Indexed: 12/14/2022]
Abstract
PURPOSE The purpose of this study was to determine whether susceptibility tensor imaging (STI) could overcome limitations of current techniques to detect tubules throughout the kidney. METHODS Normal mouse kidneys (n = 4) were imaged at 9.4T using a three-dimensional gradient multi-echo sequence (55-micron isotropic resolution). Phase images from 12 orientations were obtained to compute the susceptibility tensor. Diffusion tensor imaging (DTI) with 12 encoding directions was compared with STI. Tractography was performed to visualize and track the course of tubules with DTI and STI. Confocal microscopy was used to identify which tubular segments of the nephron were detected by DTI and STI. RESULTS Diffusion anisotropy was limited to the inner medulla of the kidney. DTI did not find a significant number of coherent tubular tracks in the outer medulla or cortex. With STI, we found strong susceptibility anisotropy and many tracks in the inner and outer medulla and in limited areas of the cortex. CONCLUSION STI was able to track tubules throughout the kidney, whereas DTI was limited to the inner medulla. STI provides a novel contrast mechanism related to local tubule microstructure and may offer a powerful method to study the nephron.
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Affiliation(s)
- Luke Xie
- Center for In Vivo Microscopy, Department of Radiology, Duke University Medical Center, Durham, North Carolina, USA; Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
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Ohno Y, Birn H, Christensen EI. In vivo confocal laser scanning microscopy and micropuncture in intact rat. Nephron Clin Pract 2006; 99:e17-25. [PMID: 15637463 DOI: 10.1159/000081794] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2004] [Accepted: 07/14/2004] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Intravital microscopy theoretically provides the optimal conditions for studying specific organ functions. However, the application of microscopy in intact organs in vivo has been limited so far due to technical difficulties. The purpose of this study was to establish a method of in vivo confocal laser scanning microscopy (CLSM) for the study of endocytosis in proximal tubules of intact kidney. METHODS The left kidney of rats placed on a modified microscope stage was exposed and stabilized in a thermostatically controlled cup. The stage was then attached to an upright confocal microscope. Surface proximal tubules were microinfused with fluorescent albumin or transferrin. Single or time-series images of microinfused proximal tubules were recorded in reflection and/or fluorescence mode. RESULTS The stability of the kidney and the resolution of images were sufficient to visualize intracellular vesicles. Albumin and transferrin were initially observed at the brush border, then later internalized by proximal tubules and accumulated in lysosomes over a time period of 15 min. Furthermore, fusion of vesicles was observed in time-lapse images. CONCLUSION These results show that in vivo CLSM in intact kidney may be an excellent method to evaluate proximal tubular endocytosis and ligand trafficking.
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Affiliation(s)
- Yoshio Ohno
- Department of Cell Biology, Institute of Anatomy, University of Aarhus, Aarhus, Denmark
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Du Z, Duan Y, Yan Q, Weinstein AM, Weinbaum S, Wang T. Mechanosensory function of microvilli of the kidney proximal tubule. Proc Natl Acad Sci U S A 2004; 101:13068-73. [PMID: 15319475 PMCID: PMC516518 DOI: 10.1073/pnas.0405179101] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Normal variations in glomerular filtration induce proportional changes in proximal tubule Na+ reabsorption. This "glomerulotubular balance" derives from flow dependence of Na+ uptake across luminal cell membranes; however, the underlying physical mechanism is unknown. Our hypothesis is that flow-dependent reabsorption is an autoregulatory mechanism that is independent of neural and hormonal systems. It is signaled by the hydrodynamic torque (bending moment) on epithelial microvilli. Such signals need to be transmitted to the terminal web to modulate Na+-H+-exchange activity. To investigate this hypothesis, we examined Na+ transport and tubular diameter in response to different flow rates during the microperfusion of isolated S2 proximal tubules from mouse kidneys. The data were analyzed by using a mathematical model to estimate the microvillous torque as function of flow. In this model, increases in luminal diameter have the effect of blunting the impact of flow velocity on microvillous shear stress and, thus, microvillous torque. We found that variations in microvillous torque produce nearly identical fractional changes in Na+ reabsorption. Furthermore, the flow-dependent Na+ transport is increased by increasing luminal fluid viscosity, diminished in Na+-H+ exchanger isoform 3 knockout mice, and abolished by nontoxic disruption of the actin cytoskeleton. These data support our hypothesis that the "brush-border" microvilli serve a mechanosensory function in which fluid dynamic torque is transmitted to the actin cytoskeleton and modulates Na+ absorption in kidney proximal tubules.
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Affiliation(s)
- Zhaopeng Du
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520-8026, USA
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Zhai XY, Birn H, Jensen KB, Thomsen JS, Andreasen A, Christensen EI. Digital three-dimensional reconstruction and ultrastructure of the mouse proximal tubule. J Am Soc Nephrol 2003; 14:611-9. [PMID: 12595496 DOI: 10.1097/01.asn.0000051725.00406.0c] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Mice are prime targets of experimental gene modification and have become object of an increasing number of biologic studies in renal physiology, development, and molecular biology. Phenotypic changes in response to gene modification require detailed information on normal structure. However, detailed analyses of normal mouse kidney structure and organization are lacking. This study describes the 3D organization and ultrastructural, segmental variation of the mouse kidney proximal tubule. A total of 160 proximal tubules in three C57/BL/6J mouse kidneys were analyzed on 800 serial sections from each kidney from the surface to the inner stripe of the outer zone of medulla. All tubules were reconstructed in 3D and visualized by interactive computer graphics. A quantitative ultrastructural analysis of the mouse proximal tubule at every 300 to 400 micro m was performed. The 3D representation revealed a distinct organization of the mouse proximal tubule, each occupying a separate domain within the cortex. Superficial proximal tubules have long straight parts converging into clusters within the medullary rays. Tubules originating deeper within the cortex become longer and increasingly tortuous. In the medullary rays, these are arranged in layers outside the clusters of more superficial tubules. In contrast to rat and human kidney, no major segmental variation in the ultrastructure of the proximal tubule was identified, and no parameters enabled definition of distinct segments in this strain of mice. In conclusion, significant new information on the 3D organization of the murine proximal tubule has been obtained. Quantitative, ultrastructural analyses of mouse proximal tubules reveal substantial differences compared with other species.
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Affiliation(s)
- Xiao Yue Zhai
- Department of Cell Biology, Institute of Anatomy, University of Aarhus, Denmark
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